Veteran endurance swimmer Diana Nyad has defended her 110-mile record feat from Cuba to Florida after sceptics questioned whether she got into or held on to a boat during part of the journey.

Ms Nyad, 64, said she swam without holding on to any of the boats or people accompanying her. "I swam. We made it, our team, in squeaky-clean, ethical fashion," she said.

Her critics are suspicious about long stretches of the 53-hour swim when Ms Nyad appeared to have either picked up incredible speed or to have gone without food or drink.

Since Ms Nyad finished her swim on September 2 in Key West, long-distance swimmers have been debating it on social media and in online forums.

Her speed, at some points more than doubling, has drawn particular scrutiny. Her team has attributed her speed to the fast-moving Gulf Stream flowing in her favour.

The athlete and her team held a conference call with some of the sceptics who questioned her navigator's credentials and observations of the currents. "Many of us are pursuing this as a technical matter," said kayaker and lawyer Richard Clifford. "Having the information out there helps us analyse it, measure it, test it, smell it, you know, decide if it looks right and is right, and you guys keep saying it is. So, let us look at it."

Ms Nyad's navigator, John Bartlett, said her fastest speed averaged about 3.97mph over a 5.5-hour period over about 19 miles, crossing the strongest parts of the Gulf Stream, which was flowing at a favourable angle. "What you're seeing is the combination of the speed of Diana propelling herself in the water and the speed of the current carrying us across the bottom," he said.

Evan Morrison, co-founder of the online Marathon Swimmers Forum, says it will be interesting to compare observations made by Ms Nyad's navigator with publically-available data about the currents she swam.

Ms Nyad attempted the swim from Cuba to Florida four times before finally completing the journey on her fifth attempt, making her the first to make it without the aid of a shark cage.

She did follow a streamer dangled in the water by her team and used a specialised mask and bodysuit to protect herself from venomous jellyfish, which are considered a more serious threat than sharks in those waters. Some members of the marathon swimming communities say these methods were against the traditions of her sport.